Extended nitric oxide measurements in exhaled air of cystic fibrosis and healthy adults.

In cystic fibrosis (CF) lung disease, exhaled nitric oxide (FeNO) is not raised, but rather is normal or even decreased when measured at a single expiratory flow. FeNO measurements at several flow rates allow differentiation between alveolar and bronchial nitric oxide (NO) production. Extended FeNO measurements therefore should be useful to localize the FeNO deficit in CF airways.